High molecular weight organopolysiloxanes, such as gums and elastomers which were prematurely or partially cured have been discarded as waste materials. Since these materials are relatively expensive, it would be desirable to convert these materials to a form in which they could be utilized.
It is known that waste materials, such as high molecular weight organopolysiloxanes and gums which have been prematurely or partially cured as well as elastomers which are based on linear organopolysiloxanes may be converted to cyclic organopolysiloxanes. According to U.S. Pat. No. 2,934,550 to Jack, cyclic dimethylpolysiloxanes can be prepared by heating a mixture consisting essentially of linear organopolysiloxanes in the presence of catalysts such as aluminum or phosphous halides, which promote the redistribution of siloxane bonds at a temperature of at least 250.degree. C. under essentially anhydrous conditions, while simultaneously distilling off cyclic organopolysiloxanes formed during the heating process.
Compared to the known process for preparing cyclic dimethylsiloxanes from essentially linear dimethylpolysiloxanes and compared to similar processes known for the utilization of waste materials containing linear or branched organopolysiloxanes comprising at least 50 mol percent of dimethylsiloxane units (U.S. Pat. No. 2,673,843, to Humphrey, et al and British Pat. No. 752,860,) the process of this invention has certain advantages. For example, it can be carried out at lower temperatures and it does not require anhydrous conditions. Moreover, it does not necessitate the separation of the catalyst which promotes the redistribution of siloxane bonds, during the distillation of the cyclic dimethylpolysiloxanes. Furthermore, the process of this invention produces higher yields of cyclic dimethylpolysiloxanes than was obtained heretofore in the same size equipment and in a shorter period of time.
Therefore it is an object of this invention to provide a process for preparing cyclic dimethylpolysiloxanes. Another object of this invention is to provide a process for preparing cyclic dimethylpolysiloxanes from high molecular weight organopolysiloxanes and elastomers. Still another object of this invention is to provide a process for preparing cyclic dimethylpolysiloxanes from waste materials containing organopolysiloxanes, gums or elastomers which have prematurely or partially cured. A further object of this invention is to provide a process for preparing cyclic dimethylpolysiloxanes from siloxane containing waste materials at lower temperatures and in greater yields.